Electron device



1960 G. R. FEASTER ET AL 2,965,793

ELECTRON DEVICE Filed May 12, 1959 Fig.|.

l/Il II/ Fig.3.

INVENTORS Gene R. Feuster 8 James L. McIntyre BY ATTJQJE Y United StatesPatent ELECTRON DEVICE Gene R. Feaster and James L. McIntyre,Horseheads, N.Y., assignors to Westinghouse Electric Corporation, EastPittsburgh, Pa., a corporation of Pennsylvania Filed May 12, 1959, Ser.No. 812,631

7 Claims. (Cl. 313-346) the nickel core cathodes have certaindisadvantages which include susceptibility to oxygen poisoning andrelatively short life.

It is, therefore, an object of this invention to provide an electrontube, the cathode of which possesses not only the combined advantages ofa solid platinum core cathode and a nickel core cathode, but alsopossesses unique advantages resulting from the combination.

It is another object of this invention to provide a cathode having ametallic core which is coated with platinum.

It is a further object of this invention to provide beam forming meanshaving a cathode with an active nickel core which is coated withplatinum.

It is an additional object of this invention to provide a cathode havingthe combined advantages of long life and low cost.

It is an auxiliary object of this invention to provide a cathode havinga means to replenish the supply of active metal within theelectron-emitting coating.

It is a supplementary object of this invention to provide a cathodewherein the nickel core and its contained reducing agents are protectedfrom undesired oxidation by a platinum coating, yet wherein the reducingagents can diffuse through the platinum during the life of the cathodeto activate the oxide electron-emitting coating.

These and other objects of this invention will be apparent from thefollowing description taken in accordance with the accompanying drawing,throughout which like reference characters indicate like parts and whichdrawing forms a part of this a plication, and in which:

Fig. 1 shows diagrammatically acathode ray tube embodying the invention;

Fig. 2 shows the portion of the electron gun of the cathode ray tubeshown in Fig. 1 adjacent the cathode;

Fig. 3 illustrates a cathode suitable for use in a receiving tube whichembodies the invention.

Although the principles of this invention are broadly applicable to allelectron tubes containing oxide cathodes, the invention is illustratedand described with particular reference to cathode ray tubes.

With specific reference to Fig. 1 there is shown a cathode ray tubeembodying the invention. The cathode ray tube of Fig. 1 comprises anevacuated envelope 1 of suitable material, glass, for example, with anenlarged conical section 2 having a faceplate 3 and a target 4 at theend thereof and a narrow neckpiece 5 in which is loice cated an electrongun 6. In Fig. 2 that portion of the electron gun 6 immediately adjacentthe cathode is shown in greater detail. The cathode 20 comprises atubular cathode core of a suitable material such as a customary cathodenickel alloy which has an elongated body portion 21 and an end closure22'. One suitable nickel alloy for the cathode core is the materialknown as active nickel. This nickel alloy contains controlled smallpercentages of various substances such as aluminum, titanium andmagnesium which migrate to the surface of the cathode core and producefree alkaline earth metals due to the reduction of the alkaline earthoxides in the coating 24. A continuous coating of metallic platinum 23is provided which covers at least the end portion 22 of the cathodecore. A coating 24 of electron emissive material, barium-strontium oxidefor example, is provided on the platinum coating 23. When the cathode isheated to a red heat, for example, by a heater, a cloud of electrons isthermionically emitted from the electron emissive surface 24. Thecathode 20 is positioned coaxially within a cylindrical controlelectrode by means of an insulating spacer ring 27. The end of thecylinder nearest the electron emitting surface 24 of the cathode 20 isclosed by a disc 25 which is positioned closely adjacent to theelectron-emitting surface of the cathode A small aperture 26 is providedopposite the cathode-emitting surface which has a considerably smallerarea than the area of the electron-emitting coating 24. An anode 35 ispositioned adjacent the control electrode which has a small aperture 36that is substantially coaxially aligned with the aperture 26 in thecontrol electrode and the cathode. The anode is maintained at a positivepotential with respect to the cathode, and a small diameter high densityelectron beam is produced by the coa'ction of the cathode 20, controlelectrode and the anode. A more detaled explanation of the operation ofan electron gun may be had by referring to US. Patent 2,773,212 issuedto James A. Hall.

In Fig. 3 is shown a cathode suitable for use in a receiving tube. Thiscathode comprises a core 31 of a customary cathode nickel alloy, acontinuous coating of metallic platnum 32 and an electron emissivecoating 33. The coating of platinum is provided at least in the area towhich the electron emissive coating 33 is applied.

to the cathode core. The platinum coating may be. appl ed to the activenickel core by any suitable method which gives intimate thermal andelectrical contact between the core and the platinum coating, such as acladding or electroplating operation, for example.

A suitable plating process can be found in Metal Finishing Guidebook,1958 edition, published by Finishing Publications, Inc., Westwood, NewJersey. A suitable plating solution that has been used and givessatisfactory results is as follows:

Water liter 1 Ammonium nitrate gms 100 Sodium nitrate gms 10 PlatinumP-salt (61%) gms.. l0 Ammonia (conc.) cc 50 Current density amp./sq. ft55-120 Temperature C-..

The Platinum P-salt referred to is a platinum diamrnino nitrite of theformula Pt(NH (NO and can be purchased from Baker & Company, Inc.,Newark, New Jersey.

The conventional type electron gun currently used in cathode ray tubesas, for example, television picture tubes generally comprises acylindrical cathode with a flat electron emissive surface, an aperturedmodulating electrode in close proximity to the cathode emissive surfaceand an anode in close proximity to the control electrode on the sideopposite the cathode. Further accelerating and focusing anodes may belocated after the first anode.

The principal disadvantage of this type of arrangement is that the areaof the cathode from which the electron beam is derived is relativelysmall due to the small aperture in the control electrode through whichan electric field set up by the first anode may be effective to form anelectron beam from electrons thermally emitted from the cathode. Tomaintain emission the cathode must possess a sufficiency of the activemetal, barium, for example, within its oxide matrix. Due to the factthat the active metals diffuse laterally through the alkaline earthoxide to some extent but do not diffuse through or over nickel at all,the tube life is largely determined by the life of the central portionof the cathode-emitting surface. By coating the cathode core withpatinum metal, a metal into and on which alkaline earth metals diffuseeasily, a supplementary diffusion path is offered to assist thediffusion of the active metal to the central emitting area of the oxidematrix. Thus, by this invention the peripheral, unused, electronemitting area of alkaline earth metal oxides is caused to act as asupply area of alkaline earth metals as they are depleted, by the actionof gas ions for example, from the central electron emitting area of theoxide coating and thereby achieve much longer cathode life.

To maintain the high current levels that are needed and used in ordinarytubes, this invention provides a nickel core under the platinum coatingto provide activating material i.e., reducing agents, by diffusionthrough the platinum to the barium strontium oxide coating. As iscustomary, within the nickel core, reducing agents are provided whichgive direct chemical production of barium from the matrix by reductionof the barium oxide layer. The reducing agents are dispensed graduallythroughout the life of the cathode to the coating by diffusion throughthe platinum. Furthermore, the platinum acts as a barium reservoir dueto the fact that barium is absorbed in the platinum layer and thenreleased to the oxide coating later when the content of barium withinthe oxide layer falls. To obtain this reservoir action it is generallynecessary for the depth of the platinum layer to be at least one percentof the total cathode core thickness or 25 microinches, whichever issmaller. This reservoir property also enables the cathode to recoverfrom transient oxygen attacks such as occur during the processing of atube. The platinum coating also functions to protect the nickel core andits reducing agents from oxidation, and furthermore to provide areduction of nickel sublimation within the tube since nickel sublimationpresents a substantial contribution to interelement leakage in tubes.

It will be recognized that the objects of the invention have beenachieved by providing a cathode for an electron tube having a greatlyincreased life. This cathode possesses the advantages of both a nickelcore cathode and a platinum core cathode and possesses additionaladvantages due to the dispensing action of the nickel core activatingimpurities through the platinum coating. This cathode also allowslateral migration of the active metal which replenishes the supply ofactive metal in the central electron emitting area of the cathode as itis depleted. In addition the cathode is not susceptible to poisoning dueto oxidation of the reducing agents contained in the nickel core duringprocessing.

While the present invention has been shown and described in one formonly, it Will be obvious to those skilled in the art that it is not solimited but is susceptible of various changes and modifications withoutdeparting from the spirit and scope thereof.

We claim as our invention:

1. A cathode comprising a nickel core, a coating of platinum thereon,and a coating of electron emissive material thereupon.

2. In a cathode ray tube including an evacuated envelope, a target atone end thereof, and an electron gun for forming and focusing a beam ofelectrons upon said target, a cathode for supplying electrons for saidbeam comprising a nickel core, a coating of platinum thereon and acoating of electron emissive material provided over said platinumcoating.

3. An electron beam forming means comprising a cathode, a controlelectrode and an anode, said cathode comprising a nickel core having acoating of platinum thereon and a coating of electron emissive materialprovided over said platinum coating, said electrodes having an aperturetherein coaxial with said cathode, said anode maintained at a positivepotential with respect to said cathode, said cathode, said controlelectrode, and said anode cooperating to form an electron beam.

4. A cathode comprising a tubular nickel core having one end closed, acoating of platinum on at least said end of said core, and a coating ofelectron emissive material applied upon said platinum coating.

5. A cathode comprising a tubular nickel core, a layer of platinum cladon said core, and a coating of bariumstrontium oxides upon said platinumcoating.

6. A cathode comprising a tubular nickel core, a layer of platinum inintimate electrical and thermal contact with said core, said platinumlayer having a thickness of at least one percent of the thickness ofsaid core, and ,a coating of barium-strontium oxide upon said platinumlayer.

7. A cathode comprising a tubular nickel core, a layer of platinum inintimate electrical and thermal contact with said core, said platinumlayer having a thickness of at least 25 microinches, and a coating ofbarium-strontium oxide upon said platinum layer.

References Cited in the file of this patent UNITED STATES PATENTS2,192,491 Widell Mar. 5, 1940 2,744,838 Newman May 8, 1956 2,830,917Kern Apr. 15, 1958 2,848,644 Koppius Aug. 19, 1958 2,867,742 LemmensJan. 6, 1959 FOREIGN PATENTS 910,133 France Ian. 21, 1946

